The lack of reactivity to environmental stimuli is regarded as a significant feature of major depressive illness. Although affective and psychomotor "deficits" have been identified, the cognitive aspects of reactivity remain poorly understood. As a result, an integrative view of reactivity that includes affective, psychomotor and cognitive properties has not yet emerged. Using facial electromyography (EMGs), this study seeks to evaluated cognitive reactivity among fifty hospitalized depressives and fifty normal controls. In particular, we will assess whether EMGs support the distinction between cognitive and affective reactivity; whether depressives and normals have distinct cognitive reactivity profiles; whether reactivity can be experimentally induced; and, whether there is increased reactivity following clinical improvement. To assess reactivity, non-invasive surface electrodes will be attached to the mentalis ("oral"), corrugator ("grief") and zygomatic ("smile") facial muscle regions. Potential confounding variables such as sex, age, handedness and severity of depression will be controlled. Using a repeated measures experimental design, subjects will first be asked to image past happy, sad and "typical day" situations; they will subsequently be exposed to explicit statements intended to prime personal knowledge of happy, sad and typical day situations; and, they will then be asked to repeat the imagery tasks. EMG testing will be conducted at admission and discharge, enabling us to assess changes in reactivity for inpatients following clinical improvement. This study would expand a unique database in an area that promises to increase the understanding of the underlying pathophysiology of affective and cognitive dysfunction in depression.